Multiple populations in Galactic globular clusters: a survey in the Str\"omgren system

We are coming to believe that stellar populations in globular clusters are not as simple as they were once thought to be. A growing amount of photometric and spectroscopic evidence shows that globular clusters host at least two different stellar populations. In our contribution to these proceedings we present the first results of a survey we are conducting to look for the presence of multiple populations in a significant number of Galactic globular clusters, using the Str"omgren system. We intend to photometrically separate these populations and characterize their radial distributions and extensions.